The present invention relates to a clutch mechanism for a push-button type tuner and, more particularly, to a clutch mechanism for a tuner of the push-button type capable of correctly maintaining the position of a tuning core which is variable with respect to a coil body.
Such a tuner has been well known as having both a push-button type tuning mechanism adapted to cause a change in inductance by a selective depression of push-buttons and an additional manual tuning mechanism having a manually operative tuning shaft adapted to be rotated to change the inductance.
In such a tuner, the change in the inductance is effected by changing the position of a tuning core with respect to the coil body of the tuner either by depressing push-buttons or by rotating the manual tuning shaft. In order to correctly maintain the core at the selected position, after the position of the core is selected, a clutch mechanism is incorporated in such a tuner.
In those tuners which must be constructed to be compact and small, as is the case of push-button type tuners, the stroke of the tuning core for a given frequency range becomes inevitably small so that the allowable range of deviation of the core is made correspondingly small. Thus, the core is apt to get out of the allowable range due to an application of external forces, e.g. vibration or the like.
In order to avoid this, it is strictly required to insure the maintainance of a correct position of the core. Consequently, in substantially the above described type of tuner, a declutch arrangement has been provided which decouples the manual tuning shaft when a push-button is depressed. The arrangement usually includes a crown gear mounted on one end and a disc having a friction ring bonded thereto on the other end of a sleeve received on a drive shaft coupled to a treadle bar through intermeshing gear members, and another disc contacting the first disc by means of the friction ring is mounted on the other edge of the drive shaft. A finger like end of a declutch bar is received in the circumferential recess of the sleeve. A coil spring received on the drive shaft sandwitched between the sleeve and a side plate of a tuner frame through which the drive shaft extends and is journaled thereon, provides the proper force against the sleeve to cause the two discs to make firm engagement with the friction ring therebetween. The manual tuning shaft is coupled to the crown gear through a pinion connected to the former. Rotation of manual tuning shaft imparts rotation to the crown gear to in turn rotate the drive shaft. The declutch bar moves the sleeve toward the frame against the biasing force of the coil spring upon the depression of the push-button, whereby the two discs are disengaged with the resultant decoupling of the manual tuning shaft from the rotatable drive shaft.
As has been described, in a push-button type tuner incorporating both of the push-button and manual tuning mechanisms, the push-button type tuning mechanism must be provided with a clutch mechanism, i.e. means for disengaging the two discs from each other. In Addition, means are necessary for holding the core at the right position, after it has been moved to the position for varying the inductance.
Thus, the two discs have a substantial significance in maintaining a correct position of the core. This is especially true in the case of a radio for an automobile, in which a push-button type tuner is used under a severe condition, which necessitates the use of relatively large discs, as well as a friction ring, so as to avoid slippage between the two discs. The large sizes of the discs are unacceptable from the view point of current commercial demand which requires small size and light weight for the radio receivers.
Another solution previously proposed is to use a stronger compression coil spring to increase the force with which the two discs are pressed each other. However, such a spring inconveniently requires a stronger force to be applied for depressing the buttons during the operation for changing the inductance.
This invention is devised to provide a solution to those problems, and is based on the results of a series of studies for solving these problems. It is an object of the invention to provide an improved declutching arrangement for a push-button type tuner which makes it possible to decouple the manual tuning shaft upon depression of one of the push-buttons provided therein, wherein the correct maintenance of the core position is ensured.
It is another object of this invention to provide a simple declutch mechanism equiped with lever means which performs a smooth and accurate declutching operation of a push-button type tuner.
It is still another object of the invention to provide a declutch mechanism which is relatively small in size and which is less expensive and contributes to a reduction of the production cost of the tuner.
Other and further objects, features and advantages of the invention will appear more fully from the following description.